JPH0555748B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to the structure of an adiabatic piston in an adiabatic engine or the like.

[Conventional technology]

Conventionally, engine parts such as heat-insulating pistons using ceramic materials as heat insulating or heat-resistant materials are disclosed in, for example, Japanese Utility Model Application Publication No. 59-113557 and Japanese Patent Application Laid-open No. 60-93161.
It is disclosed in the publication number etc.

First, the structure of the piston disclosed in Japanese Utility Model Application Publication No. 59-113557 will be outlined with reference to FIG. In FIG. 2, a closed space is formed between the lower surface side of a ceramic crown portion 21 having a combustion chamber 29 on its upper surface and a piston ring groove 27 on its peripheral wall, and the upper surface side of a metal skirt portion 22 having another piston ring groove 28 on its peripheral wall. The ceramic crown part 21 and the metal skirt part 22 are connected by a fastening bolt 26 so as to form a part 23, and the end of the piston pin insertion hole 24 that opens in the circumferential surface of the metal skirt part 22 is connected. A piston 20 is shown in which a seal member 25 can be freely fitted.

Further, the structure of the heat insulating piston disclosed in Japanese Patent Application Laid-Open No. 60-93161 will be outlined with reference to FIG. In FIG. 3, the structure of the adiabatic piston is indicated generally by the numeral 30. Regarding the structure 30 of this heat-insulating piston, a fitting hole 33 is provided at the upper end of the piston body 32 including the piston skirt portion.
A protrusion 34 formed on the crown 31 is fitted into the fitting hole 33, and the area around the fitting hole 33 of the piston body 32 is heated and pressurized to join the piston body 32 and the crown 31. .

The piston body 32 is made of aluminum, malleable cast iron, etc., and the crown 31 is made of ceramics such as silicon nitride. A combustion chamber 37 is formed in the protrusion 34 of the crown 31, and a protrusion 35 is formed on the outer periphery of the crown 31. Furthermore, a heat insulating material 36 made of ceramic fiber or stainless mesh is placed in the cavity 38 formed between the protrusion 34 and the protrusion 35.
It is fixed in a sandwiched state between the crown 31 and the piston body 32.

[Problem that the invention seeks to solve]

However, it is extremely difficult to obtain sufficient heat-insulating properties in heat-insulating engine members such as pistons that utilize the above-mentioned ceramic materials as heat-insulating or heat-resistant materials. The ceramic material is exposed to high temperatures on the combustion chamber side, and is therefore subjected to heat shock, which poses problems in terms of the strength of the ceramic material. Additionally, if the thickness of the ceramic material on the wall is increased for insulation purposes, the heat capacity will increase, and during the intake stroke, the intake air will receive more heat from the combustion chamber and become hotter, and this heat will affect the intake air, reducing intake efficiency. However, on the other hand, there is a problem in that the heat insulation must be improved during the expansion stroke.

By the way, regarding the structure of the piston disclosed in the above-mentioned Japanese Utility Model Publication No. 59-113557, the crown portion 2
1 is a ceramic material, which is extremely thick and therefore has an extremely large heat capacity, causing the above-mentioned problem. Furthermore, the crown portion 21
Since the combustion chamber 29 is formed therein, there is a problem in that the thickness of the crown portion 21 must be made thick from the viewpoint of structure and strength.

Further, regarding the structure of the heat insulating piston disclosed in the above-mentioned Japanese Patent Application Laid-open No. 60-93161, Crown 31
In other words, the joint between the piston body 32 and the piston body 32,
The sealing function of the joint of the heat insulating material 36 interposed between the two is insufficient, and the heat insulating property on the combustion chamber side is also not sufficient, and the thickness of the crown 31 made of ceramics is as described above. Similarly, it is extremely thick and is configured to be directly exposed to the combustion chamber 37 side, so it has a large heat capacity and also suffers from strength problems as it receives heat shock.

The purpose of this invention is to solve the above-mentioned problems, and to obtain an extremely high degree of heat insulation and to reduce the heat capacity of the surface of the piston head facing the combustion chamber, which is exposed to combustion gas and becomes hot. The structure is as small as possible, improving suction efficiency and cycle efficiency,
In addition, there will be no strength problems even when exposed to heat shock, improving heat resistance, corrosion resistance, and deformation resistance.In addition, a stable mounting condition can be obtained, and the pressure applied to the piston head in the event of an explosion It is an object of the present invention to provide a structure of an adiabatic piston in an adiabatic engine, etc., which can receive the piston in a preferable state and improve the sealing function between the piston head and the piston skirt.

[Means for solving problems]

In order to achieve the above object, the present invention is configured as follows. That is, the present invention provides a piston in which a mounting boss portion formed on a piston head portion is fitted into a mounting hole formed on a piston skirt portion to be fixed, in which an upper surface of the peripheral portion of the piston skirt portion is attached to a peripheral portion of the piston head portion. a ring made of ceramic material that is held in a pressed state;
A flat thin thin plate made of ceramic material that constitutes the surface exposed to combustion gas joined to the ring, the upper surface of the piston head, the lower surface of the thin plate, and the inner circumferential surface of the ring. The present invention relates to a structure of a heat insulating piston, characterized in that it is composed of a heat insulating material sealed in a space formed by.

Further, in the structure of this heat insulating piston, the peripheral portion of the thin plate and the ring are joined by chemical vapor deposition using a ceramic material.

Further, in the structure of this heat insulating piston, the thin plate and the ring are formed as thin as possible, for example, approximately 1 mm or less, so as to minimize the heat capacity between the thin plate and the ring. It is composed of

Further, in the structure of this heat-insulating piston, a heat-insulating air layer is formed between the piston head portion and the piston skirt portion.

Further, in the structure of this heat insulating piston, the upper surface of the piston head portion is formed in a flat shape.

Further, in the structure of this heat-insulating piston, the piston head portion is made of cermet, which is a material having a coefficient of thermal expansion substantially equal to that of the ceramic material.

Further, in the structure of this heat insulating piston, the thin plate and the ring are made of silicon nitride.

Further, in the structure of this heat insulating piston, a carbon seal gasket is interposed on the contact surface between the ring and the piston skirt portion.

[Effect]

The structure of the heat insulating piston according to the present invention is constructed as described above, and operates as follows. That is, in this invention, a piston head portion made of a material having a coefficient of thermal expansion approximately equal to that of a ceramic material is attached to a piston skirt portion, and a flat ceramic thin plate is attached to the piston head portion via a heat insulating material. Therefore, the thickness of the thin plate located on the surface of the piston head, which is exposed to combustion gas and becomes high temperature, can be made thin, the heat capacity of the thin plate can be made as small as possible, and a high degree of heat insulation can be achieved. properties, deformation resistance, and corrosion resistance, and can improve suction efficiency and cycle efficiency.

That is, the thinner the thickness of the thin plate, the better the ability to follow the gas temperature, that is, the wall temperature amplitude between high temperature and low temperature inside the combustion chamber is larger than when the thickness is thick. As a result, the temperature difference between the combustion gas and the thin plate becomes smaller, and the amount of heat transfer decreases, thereby reducing the heat received by the intake air.

Moreover, even if subjected to a heat shock, no strength problems will occur, heat resistance, deformation resistance, etc. can be improved, a stable mounting condition can be obtained, and the pressure acting on the thin plate during an explosion can be reduced to a preferable level. The sealing function between the piston head portion and the piston skirt portion can also be improved.

〔Example〕

Hereinafter, embodiments of the structure of the heat insulating piston according to the present invention will be described in detail with reference to the drawings.

In FIG. 1, the structure of an adiabatic piston according to an embodiment of the invention is indicated generally by the numeral 10. The adiabatic piston structure 10 mainly consists of a piston head part 1 and a metal piston skirt part 2. The piston head part 1 has a mounting boss part 4 in the center, and is made of a material such as cermet, metal, etc., which has a coefficient of thermal expansion almost equal to that of ceramic material, has high strength, and has a relatively high Young's modulus. has been done.

A combustion chamber is not formed in the piston head part 1 itself, and the combustion chamber 1 of the piston head part 1 is
The fifth side is configured in a flat or planar shape. A central mounting hole 12 is formed in the center of the piston skirt portion 2, into which the mounting boss portion 4 of the piston head portion 1 is fitted. The mounting boss portion 4 of the piston head portion 1 is located in the center mounting hole 1 of the piston skirt portion.
2, the metal ring 1 is fitted over the fitting groove 14 formed in the mounting boss part 4 and the fitting groove 13 formed in the central mounting hole 12 of the piston skirt part 2.
1 is deformed and housed, so that the piston head portion 1 is locked against the piston skirt portion 2 in a pressed state.

Furthermore, a cushioning material 8, which is a heat insulating gasket, is interposed in a pressed state at the center abutment area between the piston head portion 1 and the piston skirt portion 2, and this cushioning material 8 also has a heat insulating function. Moreover, between the piston head part 1 and the piston skirt part 2,
A heat insulating air layer 9 is formed.

The structure 10 of this heat insulating piston has the above-mentioned structure, and is particularly characterized by the following structure.
That is, the ceramic thin plate 5 made of ceramic material
In order to reduce the heat capacity of
is formed extremely thin, and the thin plate 5 is formed in the combustion chamber 15.
It is arranged on the piston head part 1 with a heat insulating material 3 in between so as to face the piston head. The thin plate 5 is made of ceramics such as silicon nitride, and is manufactured to have a thickness of about 1 mm or less.

A ceramic ring 6 made of a ceramic material made of the same material is fitted to the outer peripheral portion of the thin ceramic plate 5. The thin ceramic plate 5 and the ceramic ring 6 are, for example, 1
They are bonded by CVD (Chemical Vapor Deposition) at the contact portion shown at 8. A stepped portion 16 is formed on the inner peripheral surface of the ceramic ring 6, and the piston head portion 1
The outer periphery 17 of the ceramic ring 6 is a stepped portion 16.
It is fitted into the ceramic ring 6 so as to come into contact with the ceramic ring 6.

A heat insulating material 3 is enclosed in a space formed by the thin ceramic plate 5, the ceramic ring 6, and the piston head 1. This insulation material 3
is made of materials such as potassium titanate whiskers and zirconia fibers, and performs a heat insulating function and functions as a structural member that absorbs the pressure that acts on the ceramic thin plate 5 during an explosion.

By attaching the piston head portion 1 to the piston skirt portion 2 in a pressed state, the outer peripheral portion 17 of the piston head portion 1 is pressed against the stepped portion 16 of the ceramic ring 6, and the ceramic ring 6 is pressed against the piston skirt portion 2. is pressed by the surrounding area. Further, it is preferable that the thickness of the portion of the ceramic ring 6 facing the combustion chamber 15 be as thin as possible.
In this case, a carbon seal 7, which is a gasket, is interposed to seal between the ceramic ring 6 and the piston skirt portion 2. The seal axial force on the carbon seal 7 is exerted by the piston head portion 1 being attached to the piston skirt portion 2 in a pressed state.

In the structure 10 of this insulating piston, the compressive force caused by the explosion must be evenly received by the insulating material 3 such as potassium titanate or a heat-resistant material with large porosity. The surface and the thin ceramic plate 5 are constructed in a flat shape.

〔Effect of the invention〕

Since the structure of the heat insulating piston according to the present invention is configured as described above, it has the following unique effects. That is, the structure of this adiabatic piston is
A piston head made of a material with a coefficient of thermal expansion almost equal to that of ceramic material is attached to the piston skirt, and a flat thin plate made of ceramic material is attached to the piston head via a heat insulating material, so that combustion gas The thickness of the thin plate on the surface of the piston head, which is exposed to high temperatures when exposed to heat, can be made thinner, the heat capacity can be made as small as possible, and an extremely high degree of heat insulation can be obtained, which improves suction efficiency and cycle efficiency. can be improved.

That is, the thinner the thin plate is, the better the thin plate can follow the gas temperature. That is, the wall temperature amplitude between high temperature and low temperature inside the combustion chamber is greater than when the thickness is thicker. As a result, the temperature difference between the combustion gas and the thin plate becomes smaller, and the amount of heat transfer decreases, thereby reducing the heat received by the intake air.

Furthermore, the thin plate is directly exposed to the piston head which is exposed to high temperatures on the combustion chamber side of the engine, which improves heat resistance, deformation resistance, corrosion resistance, etc., and reduces heat shock. Even if the thin plate is subjected to an explosion, there will be no problem in terms of strength, a stable mounting condition can be obtained, and the pressure acting on the thin plate at the time of an explosion can be received in a favorable condition. Further, the thin plate and the cermet piston head have approximately the same coefficient of thermal expansion, and the piston head has high rigidity, so that
There is no problem in the connection state between the piston head part and the piston skirt part,
Even when high pressure is applied, it is difficult to deform, and the bonding state between the two is stable. Moreover, gas sealing at the boundary can be stably achieved, and the sealing function can be improved.

Further, a heat insulating material made of a ceramic material is interposed between the thin plate and the piston head, and a heat insulating air layer is formed between the piston head and the piston skirt, and the heat insulating material For example, potassium titanate whiskers,
Since it can be made of zirconia fiber, etc., or a mixture of these and glass fiber, it has a high-performance insulation function for the combustion chamber of the engine, and there is no leakage of thermal energy from the combustion chamber through the piston. Energy can be trapped in the combustion chamber. Therefore, thermal energy can be effectively recovered by the energy recovery device installed downstream in the flow direction of the exhaust gas.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of the structure of a heat-insulating piston according to the present invention, FIG. 2 is a cross-sectional view showing an example of a conventional piston, and FIG. 3 is a cross-sectional view showing an example of the structure of a conventional heat-insulating piston. It is a diagram. DESCRIPTION OF SYMBOLS 1...Piston head part, 2...Piston skirt part, 3...Insulating material, 4...Mounting boss part, 5...
...Thin plate, 6...Ring, 7...Carbon seal,
8...Buffer material, 9...Insulating air layer, 10...Insulating piston structure, 12...Central mounting hole, 13,1
4... Fitting groove, 15... Combustion chamber, 17... Outer periphery of piston head.

Claims (1)

[Scope of Claims] 1. In a piston in which a mounting boss formed on a piston head part is fitted into a mounting hole formed in a piston skirt part and fixed, the piston has a mounting boss formed in a piston skirt part and a peripheral part of the piston skirt part. A ring made of ceramic material that is fixed in a pressed state on the upper surface, a flat thin thin plate made of ceramic material that constitutes the surface part exposed to combustion gas joined to the ring, and the piston head part. 1. A structure of a heat insulating piston, comprising a heat insulating material sealed in a space formed by an upper surface, a lower surface of the thin plate, and an inner circumferential surface of the ring. 2. The heat insulating piston according to claim 1, wherein the thin plate and the ring are formed as thin as possible to reduce the heat capacity of the thin plate and the ring. structure. 3. The structure of the heat-insulating piston according to claim 1, wherein a heat-insulating air layer is formed between the piston head portion and the piston skirt portion. 4. The structure of the heat insulating piston according to claim 1, wherein the upper surface of the piston head portion has a flat shape. 5. The structure of the heat insulating piston according to claim 1, wherein the piston head portion is made of cermet, which is a material having a coefficient of thermal expansion substantially equal to that of the ceramic material. 6. The structure of the heat insulating piston according to claim 1, wherein the thin plate and the ring are made of silicon nitride. 7. The structure of the heat insulating piston according to claim 1, wherein a gasket of a carbon seal is interposed on the contact surface between the ring and the piston skirt portion.